Transmission

ABSTRACT

A change-speed transmission with a shift mechanism which selectively couples a plurality of change gears one at a time to a shaft on which the gears are journalled. The shift mechanism is disposed entirely within the transmission housing and includes a shift key arranged for axial sliding movement in a groove in the shaft. A pair of axially spaced projections at one end of the key project outwardly of the groove to embrace a collar which is journalled on the shaft. The collar is axially shifted on the shaft by a rotary shift fork which engages a circular groove in the collar to selectively position the key axially of the shaft in its several gear-engaging positions. A third radial projection at the other end of the key engages a different gear in each of the several positions thereby drivingly coupling the selected gear to the shaft to provide various forward drive speeds. The end projection of the projection pair which embrace the collar is adapted to engage a reverse gear on the other end of the shaft for providing a single reverse speed. The arrangement and construction of the several gears and the shift key are such that when the key is shifted between adjacent gear-engaging positions, it always passes through a neutral position wherein no gear is drivingly coupled to the shaft. The shift mechanism includes a detent arrangement for positively establishing selected shift positions which are correlated to the gear-engaging and neutral positions of the shift key. The particular detent arrangement permits a neutral safety switch to be used with the swift mechanism without any additional parts other than the switch itself so that the engine to which the transmission is coupled may be cranked when the transmission is in any one of its several neutral positions. A modified change speed transmission is also disclosed incorporating an improved yieldable self-biasing spring shift key, gear construction and detent sector.

This application is a continuation-in-part of our copending applicationSer. No. 171,920, filed Aug. 16, 1971, entitled "Transmission" andassigned to the assignee of record herein and now abandoned.

This invention relates to transmissions and in particular to a gearshifting arrangement for an in-line transmission.

In an in-line transmission, a plurality of gears forming a change-speedgear set are journalled side-by-side on a shaft and are in constantrunning mesh with corresponding companion gears. The shiftingarrangement drivingly couples the change-speed gears to the shaft one ata time to provide the different transmission ratios. In one known typeof shifting arrangement for this type of transmission, a key is axiallyslid in a groove in the shaft on which the change gears are journalledto couple the gears one at a time to the shaft.

The present invention contemplates an improvement in the above-describedtype of transmission gear shifting arrangement. The construction of theimproved shifting arrangement permits component parts to be subassembledonto the transmission shaft without using separate attaching parts, theobject of the construction being to greatly facilitate the assembly ofthe component parts into the transmission, reducing the cost andcomplexity thereof.

A further object of the invention is to provide a manually operableshifting arrangement wherein the shift effort, while being easy andsmooth, provides sufficient "feel" to enable the operator to positivelysense the shift positions.

An additional aspect permits a neutral start safety switch to be usedwith the improved shifting arrangement without the need of additionalparts other than the switch itself.

Some additional objects of this invention are to provide a transmissionwith a change-speed gear set and key arrangement of economicalmanufacture and assembly which can be readily and smoothly shifted intoany gear from any other gear or neutral position, whicheliminatesbacklash or free wheeling of the engaged transmission, is ofcomparatively economical manufacture and assembly, has a long usefullife, and is substantially service and maintenance free.

These and other objects, features and advantages of this invention willbe apparent from the following description, appended claims andaccompanying drawings in which:

FIG. 1 is a horizontal sectional view taken substantially along thetransmission case edge flange and with the transmission cover removed.

FIG. 2 is a vertical sectional view of the transmission of FIG. 1 takensubstantially along the line 2--2 in FIG. 1.

FIG. 3 is a vertical sectional view taken along line 3--3 in FIG. 2.

FIG. 4 is a vertical sectional view taken along line 4--4 in FIG. 1.

FIG. 5 is an exploded view taken in the same direction as the view ofFIG. 1 showing the output shaft, two shift keys and the shift collar ofthe transmission of FIG. 1 shown separately therefrom.

FIG. 6 is an axial end view of a typical change gear of the transmissionof FIG. 1.

FIG. 7 is a top view of one of the two shift keys shown in FIG. 5.

FIG. 8 is a horizontal sectional view of a modified form of atransmission embodying this invention taken substantially along thetransmission case edge flange with the transmission cover removed.

FIG. 9 is a partially sectioned and partly exploded view taken in thesame direction as the view of FIG. 8 showing the output shaft, two shiftkeys and the shift collar of the transmission of FIG. 8.

FIG. 10 is an axial end elevational view of a typical change gear of thetransmission of FIG. 8.

FIG. 11 is a horizontal sectional view taken on line 11--11 of FIG. 10.

FIG. 12 is an axial end view of a typical washer which is adapted to bereceived in the change gear of FIG. 10.

FIG. 13 is a sectional view taken on line 13--13 of FIG. 8.

FIG. 14 is an enlarged fragmentary view of the output shaft of thetransmission of FIG. 8 with one of the keys received in the shaft andtwo change gears received thereon.

FIG. 15 is an enlarged side view of a shift key of the transmission ofFIG. 8.

Referring to FIGS. 1 and 2, the transmission 10 of the inventioncomprises a case 12 whose upper edge 14 mates with the lower edge (notshown) of a cover 16 to enclose the transmission mechanism. A verticalinput shaft 18 (FIG. 2) is journalled within a cylindrical bore 20 of anelongated boss 21 in the bottom wall of case 12 by needle bearings 22.The inner splined end of shaft 18 receives a bevel pinion gear 24. Gear24 is retained on shaft 18 by a retaining ring 26, and bears against athrust race 28 between itself and case 12. A second retaining ring 30and washer seal 32 on the external portion of shaft 18 retain thedescribed input arrangement on case 12.

A counter shaft 34 and an output shaft 36 (FIG. 1) are journalled in theright-hand and left-hand end walls of the transmission enclosure bymeans of flanged sealing bushings 38. Four companion spur gears 40, 42,44 and 46 and a bevel gear 48 are keyed side-by-side on counter shaft 34for rotation therewith. The five gears 40 through 48 are retained onshaft 34 between a thrust race 50 and a circular shoulder 52 on shaft34. Bevel gear 48 meshes with bevel pinion gear 24 so that rotation ofinput shaft 18 rotates all five gears 40 through 48 in unison.

Companion gears 40, 42, 44 and 46 are in constant running mesh with fourspur change gears 54, 56, 58 and 60 respectively. Change gears 54through 60 are journalled for free rotation on intermediate diametercylindrical portion 62 of output shaft 36. Gears 54 through 60 areaxially retained as a cluster on portion 62 by a shoulder 63 of shaft 36and a thrust race 65. Referring also to FIG. 6, each change gear 54through 60 has four identical arcuately extending teeth 64 which projectradially inwardly of identical circular gear bores 66 to journal thegear on shaft 36. Each tooth 64 has a 45° arcuate extent, and the fourteeth 64 are symmetrically arranged to define 45° arcuate free spaces 70between adjacent teeth. As can be seen in FIG. 1, the axial dimension ofeach tooth 64 is slightly less than one-half the axial dimension of thegear. Therefore, this construction defines an annular free space 68adjacent teeth 64 and spaces 70 which lies radially between theright-hand portion of each bore 66 and portion 62 of shaft 36. Thisstructure of gears 54 through 60 enables transmission 10 to be properlyshifted through four forward speeds as will become apparent.

Because input shaft 18 rotates in only one direction to similarly rotategears 54 through 60, a single reverse speed is provided by a sprocketand chain arrangement located adjacent the right-hand end wall. Asprocket gear 72 is keyed to shaft 34 for rotation therewith and axiallyretained thereon by a shoulder 74 and a thrust race 76. Sprocket 72drives a sprocket gear 78 on shaft 36 by means of an endless rollerchain 80, only a portion of which is illustrated in FIG. 1. Sprocket 78is journalled for free rotation on another intermediate diametercylindrical portion 82 of shaft 36 of the same diameter as portion 62,by means of four inwardly projecting arcuate teeth 84 whosecircumferential extent is the same as teeth 64 of gears 54 through 60but whose axial dimension is the same as that of sprocket 78 itself.This construction defines four 45° arcuate spaces (not shown) similar tospaces 70 of gears 54 through 60. Sprocket 78 is retained on portion 82by a circular shoulder 86 of shaft 36 and a thrust race 88.

The structure of the improved shifting arrangement of the invention canbe better understood by referring to FIG. 5 in addition to FIGS. 1 and2. Output shaft 36 further includes a maximum diameter cylindricalportion 90 between the portions 62 and 82, the axially opposite ends ofportion 90 defining shoulders 63 and 86. Two diametrically opposedrectangular grooves 92 and 94 extend axially of shaft 36 all the waythrough portions 62, 90 and 82 and have their respective flat bottomsurfaces 92' and 94' (FIGS. 4 and 5) tangent to the outer periphery ofthe minimum diameter cylindrical opposite end portions 96-98 and 100 ofshaft 36. Hence, the axially opposite ends of each groove 92 and 94 areopen and accessible for endwise insertion of two identical shift keys104 and 106 of rectangular cross-section which are slidable axially ofshaft 36 within grooves 92 and 94 respectively. The width of each key104, 106 is dimensioned to fit snugly within the rectangularcross-section of grooves 92 and 94. The length of each key 104, 106 isslightly less than the length of portion 90 of shaft 36, and the twokeys occupy the position illustrated in FIG. 1 when the transmission isin its primary neutral position. A radial projection 108 at theleft-hand end of each key (as viewed in FIG. 1) travels within theportions of grooves 92 and 94 which are coextensive with shaft portions62 when keys 104, 106 are shifted to the left from the illustratedposition. Projections 108 project radially outwardly beyond the surfaceof portion 62 and terminate just short of the inside diameter of bores66 in gears 54 through 60 to permit projections 108 to be axiallyshifted through gears 54 through 60.

With keys 104, 106 in the primary neutral position of FIG. 1,projections 108 are within the annular free space 68 of gear 60. Whengear 60 is rotated relative to shaft 36 to a position whereinprojections 108 register with diametrically opposite spaces 70 of gear60, keys 104, 106 may be shifted to the left from the positionillustrated in FIG. 1 to bring projections 108 into diametricallyopposed spaces 70 and thus between adjacent pairs of teeth 64. Furtherrotation of gear 60 causes two diametrically opposed teeth 64 to engageprojections 108 to thereby couple gear 60 in rotational driving relationto shaft 36 (first gear). Further leftward shifting of keys 104, 106disengages projections 108 from teeth 64 of gear 60 so that projections108 are now situated within space 68 of gear 58. The axial dimension ofprojections 108 being less than the axial dimension of spaces 68prevents coupling of more than one change gear at a time to shaft 36.Keys 104, 106 may be further shifted to selectively individually couplegears 58, 56 and 54 to shaft 36 in similar fashion (second, third andfourth gears). When keys 104, 106 are at their far left limit of travel,the left-hand ends of the keys are registered between teeth 64 of gear54 and flush with thrust race 65. While the illustrated construction ofteeth 64 is merely exemplary, such an arrangement provides four possiblegear engagement positions per gear revolution and prevents excessivewrap-up of shaft 36.

A shift collar 110 is journalled on portion 90 of shaft 36 and encircleskeys 104, 106 for axially shifting the keys. The right-hand portion ofeach key 104, 106 comprises two projections 112 and 114 which projectradially outwardly beyond the surface of portion 90 (and the bore 117 ofcollar 110) and are axially separated so that the collar 110 is snuglyembraced therebetween (FIG. 5). The illustrated construction providessmooth shifting performance and facilitates subassembly of keys 104, 106and collar 110 onto shaft 36. Keys 104 and 106 are first inserted withinthe collar bore, prior to assembly of these parts to shaft 36, so thatprojections 112, 114 embrace collar 110 as illustrated by the engagementof key 106 with collar 110 in FIG. 5. With the two keys held manuallydiametrically opposed relatively to the axis of collar 110, collar 110is slipped endwise over either end 96-98 or 100 of shaft 36, and rotateduntil keys 104, 106 are angularly aligned with grooves 92, 94. Collar110 may then be slid further onto shaft 36, thus inserting keys 104, 106endwise into grooves 92, 94. The keys are now securely captured on shaft36 by assembling gears 54-60, sprocket 78, thrust races 65 and 88 andbushings 38 on shaft 36 and dropping this sub-assembly into place inhousing 12.

It will be noted that projections 114, in addition to retaining collar110, serve as clutch dogs to engage the internal teeth of sprocket 78when keys 104, 106 are shifted to the right from the positionillustrated in FIG. 1 to thereby couple sprocket 78 in driving relationto shaft 36.

Returning to FIGS. 1, 2 and 4, shifter mechanism 118 comprises avertical shaft 120 journalled in .Iadd.sidewalls such as .Iaddend.theupper and lower walls of the transmission enclosure. A bifurcated shiftfork 122 having upper and lower arms 124, 126 is affixed to shaft 120.The radially outer ends of arms 124, 126 receive coaxial pins 128 and130 which project inwardly thereof to engage a central circular externalgroove 116 of collar 110. Pins 128 fit snugly within groove 116,providing only enough free play to permit collar 110 to freely revolveon and/or with shaft 36. The upper external end 132 of shaft 120 (FIG.2) is adapted to be rotated by a crank and actuator arrangement (e.g., aBowden cable) not illustrated. Counterclockwise rotation of shaft 120(as viewed in FIG. 1) shifts collar 110 axially to the left and therebysimilarly moves keys 104, 106 to successively engage gears 60, 58, 56and 54. Clockwise rotation of shaft 120 shifts keys 104, 106 to theright to engage sprocket 78 to effect reverse drive.

As best seen in FIGS. 1 and 2, a sector plate 134 is affixed to theupper portion of shaft 120 within the transmission enclosure. The outerarcuate edge 136 of plate 134 is concentric with shaft 120 and isprovided with a plurality of nine angularly spaced notches or detentseats 138 through 154 which are numbered in increasing order in theclockwise direction as viewed in FIG. 1. As better seen in FIG. 3, seats138 through 154 are adapted to be engaged by a detent ball 156 which isbiased inwardly toward plate 134 by a spring 158. Ball 156 and spring158 are situated within an opening 160 in cover 16, and the force ofball 156 against plate 134 is set by an adjustment screw 162 which isthreaded into opening 160. The engagement of ball 156 with the seats 138through 154 is correlated to the axial position of keys 104, 106 asfollows.

With transmission 10 in the position illustrated in FIG. 1, ball 156engages detent 140, thus establishing the primary neutral position. Whenshaft 120 is rotated clockwise to engage ball 156 with seat 138,projections 114 of keys 104, 106 drivingly connect sprocket 78 to shaft36, thus establishing the reverse position. Further clockwise movementof plate 134 is prevented by abutment of the chamfered corner 155adjacent seat 154 with an internal stop (not shown) on cover 16. Whenshaft 120 is rotated counterclockwise to engage ball 156 with seat 142,projections 108 of keys 104, 106 drivingly connect gear 60 to shaft 36,establishing first or low forward speed. Further counterclockwiserotation of shaft 120 to engage ball 156 with seat 144 causesprojections 108 to disengage gear 60 and to shift into space 68 of gear58, thus providing an intermediate neutral position between first andsecond speed. Similarly, engagement of ball 156 with seats 146, 150 and154 establishes second, third and fourth forward speeds respectively byengaging projections 108 with the teeth 64 of gears 58, 56 and 54respectively in that order. Movement of plate 134 beyond fullcounterclockwise position (i.e., engagement of ball 156 with seat 154)is prevented by abutment of the left-hand ends of keys 104, 106 withthrust race 65. Seats 148 and 152 define additional intermediate neutralpositions between second/third and third/fourth forward speeds.

The transmission thus far described combines an easy, smooth shifteffort having sufficient "feel" to enable the operator to sense theindividual shift positions with a rugged operational capability. Itshould be understood, however, that it may sometimes be desirable tomodify this arrangement. For example, the intermediate neutral detents144, 148 and 152 could be removed so that when shifting between firstand fourth forward speeds, the operator would "feel" only the positionswherein a drive connection is actually established. The arcuatedimensions of teeth 64 may be varied to enlarge or decrease the size ofspaces 70 into which projections 108 may be shifted. Moreover, thenumber of available gear ratios may be made more or less, and in somearrangements the number of grooves and shift keys required may bechanged with corresponding changes in the change gears to receive therevised number of keys. For example, three axial grooves may be provided120° apart for three shift keys and three teeth may be provided in gears54 through 60 to define three arcuate key-receiving openings.Furthermore, the change gears and shifting arrangement could be providedon the counter shaft 34 rather than in the output shaft 36.

Referring now to FIGS. 1 and 3, four circular holes 163a, b, c and d areprovided in plate 134 radially inwardly of detent seats 140, 144, 148and 152 respectively. Operation of shift mechanism 118 to any neutralposition wherein ball 156 engages one of seats 140, 144, 148 and 152moves plate 134 such that the hole 163 radially inwardly of that oneseat is directly below the actuator 164 of a neutral start safety switch166 which is threaded into a hole 167 in cover 16. Actuator 164 in theform of a sphere, is retained within switch 166 for vertical movementand is spring biased downwardly to assume the position illustrated inFIG. 3 when hole 163a is aligned therewith (primary neutral position oftransmission 10). With actuator 164 in this position, switch 166 forms aclosed circuit between terminals 168 and 170 which is interlocked withthe starting circuit to enable the engine which drives transmission 10to be cranked. When shift mechanism 118 is operated from a neutralposition to one of its gear-engaging positions (first, second, third,fourth or reverse), plate 134 forces actuator 164 upwardly out of thehole 163 with which it was engaged and maintains the actuator inretracted position in switch 166. When actuator 164 is so retracted, thecircuit between terminals 168 and 170 opens to prevent the engine frombeing cranked. In the case of a riding lawnmover, garden tractor or thelike, this safety feature prevents accidental lurching of the vehicleshould it be attempted to start the engine with the transmission inother than the neutral position.

Moveover, should the engine stall when the transmission is in second,third or fourth gear, the provision of holes 163b, c and d permits theengine to be cranked when projections 108 are shifted to the immediatelyadjacent spaces 68 of one of the gears 54, 56 or 58. Thus, after such astall, the likely angular misalignment of projections 108 with spaces 70of the change gears lying between projections 108 and the space 68 ofgear 60 which would prevent projections 108 from being convenientlyshifted to the primary neutral position is inconsequential. It is to benoted that switch 166 is the only additional transmission part requiredto provide this feature. The spring biased actuator 164 and holes 163a,b, c and d also provide an additional detent arrangement for the neutralpositions. Hence, it can be seen that detent seats 140, 144, 148 and 152are optional whenever switch 166 is employed, and that various detentarrangements may provide either the same or different detent force forthe neutral and gear-engaging positions.

Transmission 10 drives an output gear 172 on the left-hand external endof shaft 36. The load to be powered (such as the tractor axle) may beconnected to gear 172 by a chain or other drive arrangement. It is alsopreferable to provide a clutch between the engine and input shaft 18 sothat the engine may be disengaged when shifting gears. A circular rotor174 is slidably keyed to the right-hand external end of shaft 36. Ifdesired, a conventional disc brake assembly (not shown) may be attachedto case 12 below shaft 36 so as to support a pair of brake pads onopposite sides of rotor 174. Such a disc brake usually has an actuatorlever operated to cam the brake pads into gripping relation with rotor174 to provide a braking torque on shaft 36, as is well understood inthe art.

In the transmission thus described, change gears 54 through 60 arepreferably constructed of a sintered metal comprising iron powder, whichmay have nickel content for improved impact strength. For example, oneformulation which provides satisfactory results is as follows:

MATERIAL

NI--MN--MO Pre Alloy having the composition by weight of:

NI 0.45 percent

MO 0.60 percent

MN 0.35 percent

S 0.010 percent

P 0.010 percent

FE Balance

C 0.5/0.6 percent

Density 6.7 grams/c.c. (min.)

HEAT TREAT

Harden & Draw 400°-600° F.

To RC 32-40 Apparent Hardness

Keys 104, 106 are preferably constructed from steel such as SAE 1117steel and case hardened. Alternatively keys 104, 106 may be forgedsintered metal. It has been observed that with this construction thereis less chipping of teeth 64 than occurs when gears 54 through 60 areconstructed from ordinary case hardened gear steel. Although the edgesof teeth 64 and projections 108 are preferably beveled, beveling ofteeth 64 may be unnecessary with the above-described preferredconstruction. Also, the four upright edges 186 of each projection 108and the two outer upright edges 188 of each projection 114 arepreferably beveled to reduce chipping when these edges 186, 188 contactthe internal teeth of the change gears. Preferably, the corners arerounded to a radius of between 0.015 and 0.030 inch. It should be notedthat the shaft keyways or grooves 92, 94 are entirely internal of thetransmission enclosure and hence present no sealing problem betweenshaft 36 and the transmission housing when shaft 36 is journalledtherein. In other words, portions 96 and 100 of shaft 36 are cylindricaland uninterrupted to fit closely within the associated bushings 38 sothat grease cannot escape through the bushing. Moreover, because themoving parts, including the shift and safety switch actuatingmechanisms, are all internal, they are protected from outsidecontamination. It can thus be seen that the invention provides a compactand low cost multispeed transmission which is of rugged construction.The transmission interior is preferably packed with lubricating greaseafter assembly so that minimum wear and long life of all moving partsare achieved.

FIG. 8 illustrates a modified transmission 10' embodying this inventionwhich has five forward speeds and one reverse speed, and which isgenerally similar in construction and operation to transmission 10.Transmission 10' employs the same case 12 and cover 16 as transmission10 and has a similar input shaft 18' (not shown) and countershaft 34'journalled therein. Five companion spur gears 200, 202, 204, 206 and 208and a bevel gear 48' integral with spur gear 208 are splined in coaxialside by side relation on countershaft 34' for rotation therewith. Spurgears 200 through 208 correspond generally with spur gears 40 through 46and bevel gear 48' with bevel gear 48 of transmission 10. Bevel gear 48'meshes with the bevel pinion gear 24 (not shown) fixed to input shaft18' so that the input shaft rotates all six gears 200 through 208 and48' in unison.

Companion gears 200 through 208 are in constant running mesh with fivespeed change spur gears 210, 212, 214, 216 and 218. Gears 210 through218 are journalled in coaxial side by side relation for free rotation ona cylindrical portion 62' of output shaft 36'. Gears 210 through 218 areaxially retained as a cluster or portion 62' by a shoulder 63' of outputshaft 36' and a thrust race or washer 65. As shown in FIGS. 11 and 12,each change gear 210 through 218 has an axial bore 220 therethroughadapted to receive cylindrical portion 62' of shaft 36' for freerotation of the gear thereon, and a counterbore 222 in one face thereofin which a flat washer 224 is located either by mere seating in thecounterbore so as to be readily removable, or being fixed in thecounterbore as by brazing or sintering to the gear face. Each changegear has four symmetrically arranged arcuate slots or free faces 228 inbore 220 which extend axially through the gear and terminatecircumferentially at generally radially extending opposed end walls 230and 232. Interposed between slots 228 are four integral teeth 64' whichin assembly slidably bear at their peripheral face on output shaft 36'.Each free space or slot 228 has a generally arcuately extending step 234therein and a shift key retaining slot 236 extending generally radiallyoutwardly of step 234, the junction of step 234 with slot 236 beingdefined by an abutment wall 238 extending radially and axially of thegear. Washer 224 (FIG. 12) has a bore 239 with an inside diameter equalto that of bore 220 of the speed change gear and thus covers one axialend of each slot 228.

Gears 210 through 218 are selectively coupled for rotation with outputshaft 36' by two identical shift keys 104' and 106' each of which has acantilever spring arm 240 yieldably biasing generally radially outwardlyof shaft 36', a projection or lug 108' located adjacent the free end ofthe key. Lugs 108' each have camming ramps which slidably engage withwashers 224 in response to axial movement of the key lug through thechange gears 210-218 to selectively and individually connect anddisconnect these change gears with shaft 36'. Thus, as best seen in FIG.15, each lug 108' has two ramps 242 and 244 inclined toward each other,extending generally radially outwardly and convergently terminating inan apex 247. Each lug 108' also has a ramp 246 having a steeper slopethan ramp 244 and extending therefrom to a generally radially extendingend face 248. Ramp 246 is located to facilitate rapid initialdisplacement of lugs 108' and prevent end face 248 from butting on theface of a washer 224.

Preferably, keys 104' and 106' are machined or die stamped from flatstock with the entire bottom edge or face of the key including thebottom edge of arm 240 lying in one plane. After machining or blankingof the key, its arm 240 is bent at 250 (FIG. 15) to incline the arm withrespect to the shank 251 (FIG. 15) of key 104' so that it is inclinedoutwardly with respect to the axis of output shaft 36' when in assembledrelation therewith with shank surfaces 253 seated flat on the bottomsurface 92' or 94' of its associated groove. Preferably, bend 250 isaxially spaced from projection or lug 112 approximately .[.250.]..Iadd.0.25 inch.Iaddend..[.inches.].. It has been found that if bend 250is immediately adjacent projection 112, the key has a tendency tofracture in use, apparently due to localized high stresses produced bybending of the key aggravated by machining marks in the key from themachining of radius 252 adjacent projection 112.

Keys 104' and 106' are shifted axially back and forth in grooves 92 and94 of shaft 36' by a shifter mechanism similar to previously describedshifter mechanism 118. Thus, a sector plate 134' is fixed to shaft 120which is connected to bifurcated shifter 122 operably coupled withcollar 110. To correlate the rotary position of shaft 120 with theneutral and gear engaging positions of the shift keys, the outergenerally arcuate edge 136' of sector plate 134' has a plurality ofdetent seats therein sequentially engageable with detent ball 156. Plate134' has a reverse detent seat 138' but only one neutral detent seat140'. Unlike plate 134, plate 134' has only one cylindrical hole 163afor actuating the neutral start safety switch 166, and it has fiveforward speed detents seats 254, 256, 258, 260 and 262 without anyneutral detent seats therebetween. To facilitate the shifting oftransmission 10' from one gear to another, detent seats 254 through 260each have two inclined ramps 264 and 266 associated therewith, anddetent seat 262 has an inclined ramp 264 associated therewith. Detentball 156, due to the bais of its spring and the shape of the seats inplate 134' tends to be self-centering in the selected seats. Thepositions of shift keys 104' and 106' are correlated with thedetentretained positions of plate 134' so that when lugs 108' arereceived in slots 228 of each speed change gear 210 through 218, thelugs are centered so they do not bear on the adjacent washers 224 (asshown in phantom in FIG. 14). This yieldable retention of keys 104',106' in centered position by detent ball 156 in the associated seat ofplate 134' prevents a wearing away of the lugs or projections 108' whichmight otherwise occur if they were allowed to have a sliding frictionalengagement with washer 224 of the adjacent speed change gear, whichrotates relative to the shift key when transmission 10' is in use.

In use, transmission 10' is shifted from one gear to another by therotation of control shaft 120 which shifts keys 104' and 106' axially inslots 92 and 94 respectively of shaft 36' while engaging and disengagingdetent 156 with the various detent seats in plate 134'. When detent 156is received in detent seat 140' of sector plate 134', transmission 10'is in neutral and shift keys 104' and 106' are in the position shown inFIG. 8. Rotation of shaft 120 clockwise (as viewed in FIG. 8) to engagedetent 156 with reverse detent seat 138' moves shift keys 104' and 106'axially to the right (as viewed in FIG. 8) and engages key lug 114 withsprocket 78, thereby coupling sprocket 78 with output shaft 36' toeffect reverse drive of the output shaft 36'.

Rotation of shaft 120 counterclockwise from reverse or neutral positionso that detent 156 engages in detent seat 254 moves shift keys 104' and106' axially to the left to couple speed change gear 218 with outputshaft 36' to effect forward drive of the output shaft in first gear.During this axial movement of keys 104' and 106' to the left, ramps 246and 244 of each lug 108' will sequentially engage the washer 224associated with gear 218 and thereby cam the lugs 108' radiallyinwardly, the resilient spring arms 240 of the associated keysdeflecting as they yieldably resist such camming action. After apex 247has cleared washer 224, arms 240 force lugs 108' radially outwardly intoslots 228 thereof if or when the lugs register therewith (as shown inbroken line in FIG. 14). In some instances, when lugs 108' are shiftedaxially into registry with the bore of a gear they will first bear onthe peripheral face of teeth portions 64' between slots 228 of the gearand then will spring radially outwardly when the closest slot 228 isbrought into angular registry with the lug as the gear rotates clockwise(as viewed in FIG. 10) with respect to shaft 36'. Thus, each lug 108'will be sprung by its associated arm 240 into a slot 228 adajcent endwall 232, strike against and momentarily slidably bear on step 234, andthen be sprung further radially outwardly into the associated retainingslot 236 where the lugs are snugly received between generally opposedradial walls 230 and 238 to thereby couple the gear with the outputshaft. However, in the event that lugs 108' of the keys are axiallyshifted into registry with gear 218 precisely when one of its slots 228is aligned with the keys, they will spring directly into the slotswithout first bearing on teeth portions 64'. When this occurs, the rateof radially outward movement of lugs 108' into slots 228 is controlledby the engagement of ramps 242 of the lugs with the inner edge of awasher 224 alone or in cooperation with step 234 of the slot.

In a similar manner, rotation of shaft 120 so that detent 256sequentially engages with detent seats 254 through 264 in sector plate134' moves keys 104' and 106' axially to the left (FIG. 8) tosequentially engage lugs 108' of the keys in an opposed pair of slots228 of speed change gears 216 through 210 to sequentially couple each ofthese gears with output shaft 36', thereby providing the second throughfifth forward speeds of transmission 10'.

Whenever transmission 10' is shifted from one forward gear to another,complete disengagement of the lugs 108' of the shift keys from one speedchange gear before reengagement of the lugs with another speed changegear is assured by the cooperation of ramps 242, 244 and 246 of the lugswith washers 224 of the speed change gears. For example, whentransmission 10' is shifted from the first forward speed change gear 218to the second forward speed change gear 216, ramps 246 and 244sequentially bear on and slide under washer 224 of gear 216, thuscamming lugs 108' of the shift keys radially inwardly to completelydisengage them from slots 228 of gear 218 before the lugs can begin tomove radially outwardly to engage in the slots of gear 216. Likewise,when transmission 10' is shifted back in the other direction from secondgear to first gear, ramps 242 bear on washer 224 of gear 216 to cam lugs108' of the shift keys radially inward to completely disengage the lugsfrom slots 228 of gear 216 before the lugs can begin to move radiallyoutward to engage in the slots 228 of gear 218.

It is also to be noted that transmission 10', unlike transmission 10,can always be readily shifted from neutral into any forward gear or fromany forward gear to another forward gear regardless of the angularrelationship of speed change gears 210 through 218 to each other. Thisis due to the provision of yieldable spring arms 240 on keys 104' and106' which permit lugs 108' during shifting of the keys to move radiallyinwardly to retract and disengage from slots 228, rather than, as intransmission 10, sliding through the slots in the gears which in manyinstances are not axially aligned with each other and thus block passageof the keys axially through the gears. Thus, transmission 10' can bereadily shifted through the forward gears without having to jog orslightly rotate the output shaft of the transmission to align the shiftkeys with the slots in the gears.

To provide adequate time for lugs 108' of shift keys 104' and 106' tomove radially outward and become fully seated or bottomed in retainingslots 236 of the speed change gears, the arcuate length of slots 228 isgreater than the transverse width or thickness of lugs 108'. Preferably,the arcuate length of slots 228 is in the range of 11/4 to 2 times andpreferably substantially 11/2 times the thickness (the verticaldimension of lug 108' as seen in FIG. 13) of the portion of lugs 108'received in the slots. However, so increasing the arcuate length of theslots would introduce excessive backlash between output shaft 36' andthe speed change gear driving the output shaft were it not for theprovision of step 234 in each slot. Wall 230 and the riser wall 238 ofstep 234 thus form a shorter retaining slot 236 and provide more closelyspaced opposed abutments for receiving lugs 108' therebetween.Preferably, the distance between walls 230 and 238 is just sufficientlygreater than the thickness of lugs 108' to provide sufficient clearancefor the lugs to slide into retaining slots 236. Hence, any backlash dueto relative angular movement between output shaft 36' and the speedchange gear is reduced to an imperceptible amount once lugs 108' of theshift keys are received in retaining slots 236. Accordingly, it will nowbe appreciated that stepped slots 228 provide both adequate time for thelugs to become fully engaged in slots 236 while simultaneouslyeliminating backlash in transmission 10'. Moreover, steps 234 in slots228 ease the entry of lugs 108' into retainer slots 236, therebyminimizing the impact and resulting shock with which the lugs bottom inslot 236, which in turn is believed to minimize wear and tear on thelugs of shift keys 104' and 106' and thereby substantially increasetheir useful life.

Another advantage of transmission 10' is the very positive 37 feel"afforded the operator when manually shifting through the forward driveshift points of transmission 10'. This yieldable resistance to shiftingis provided either entirely by the action of spring keys 104', 106' orin conjunction with the ramps 264 and 266 of sector plate 134' which oneassociated with the speed change gears 210 through 218. These rampsfunction during shifting as over-center cams tending to initially retardand then subsequently urge shifting mechanism 118' of transmission 10'from one gear to an immediately adjacent gear. This positive feel isprovided even in the absence of the detent seats by the camming ofprojections or lugs 108' of shift keys 104', 106' over a washer 224every time transmission 10' is shifted from one forward gear intoanother, neutral into a forward gear, or a forward gear into neutral.However, if the detent seats are eliminated from plate 134', it ispreferable to modify edge 136' thereof so as to be a smooth segment of aspiral to yieldably bias shift keys 104', 106' generally axially to theright (as viewed in FIG. 8) so the projections 108' thereof bear againstthe washer 224 of the engaged gear and, hence, will not bear on thewasher 224 of the speed change gear immediately to the left which willbe rotating relative to the engaged gear. This modification will thusprevent a wearing away of lugs 108' and/or washers 224 by slidingfrictional engagement therebetween. The biasing force thus developed onshift keys 104' and 106' must not, however, produce sufficient force tocam lugs 108' radially inwardly and thereby unintentionally decouple theoutput shaft 36' from the driving gear.

In the transmissions thus described, speed change gears 54 through 60and 210 through 218 are preferably constructed of a sintered metalcomprising iron powder, which may have nickel content for improvedimpact strength. One exemplary formulation which provides satisfactoryresults has been set forth previously herein.

In accordance with another feature of transmission 10', speed changegears 210 through 218 are preferably made by powdered metallurgytechniques and counterbore 222 is formed during compacting of thepowdered metal compacts from which the sintered metal gears are made. Ithas been found that, in addition to eliminating subsequent machining,configurating the compacting dies to produce the counterbore in thegreen compact produces a higher density of the powdered metal in thearea of teeth 64' and slots 228 which in turn increases the strength andimpact resistance in this area of the sintered metal gear.

In addition, when speed change gears 210 through 218 are made bypowdered metallurgy techniques, washers 224 can be pre-coated withbrazing material and placed as loose inserts directly into the cavity ofthe gear compacting mold. When the compacts are subsequently sintered,washers 224 will securely adhere to the sintered metal gear. Preferably,the washers 224 received in counterbore 222 of gears 210 through 218 aremade of a high carbon steel such as SAE 1075 steel and case hardened. Italso has been observed that there is less chipping of teeth 64 of gears54 through 60 when constructed of sintered metal rather than ordinarycase hardened gear steel. Although the edges of teeth 64 and lugs 108are preferably beveled, beveling of teeth 64 may be unnecessary with theabove-described preferred construction.

Shift keys 104, 106 and 104' and 106' are preferably constructed fromsteel such as SAE 1117 steel and case hardened. Alternatively, the shiftkeys may be forged sintered metal. Also, the two outer upright edges 188of each projection or lug 114 of shift keys 104' and 106', like keys 104and 106, are preferably beveled to reduce chipping when edges 188 engagethe speed change gears. Preferably, the corners are beveled by beingrounded to a radius of between 0.015 and 0.030 inch.

It should be noted that the keyways or grooves 92, 94 in output shaft36' of transmission 10' are entirely internal of the transmissionenclosure and, hence, present no sealing problem between the outputshaft and its associated transmission housings when the shaft isjournalled therein. Transmission 10' also retains the other advantagesof transmission 10, such as protection of the moving parts, includingthe shift and safety switch actuating mechanisms, from outsidecontamination, a compact low-cost rugged construction, minimum wear andlong life of all moving parts.

We claim: .[.1. In a transmission, the combination comprising a housing,a shaft journaled in said housing, said shaft having first and secondportions extending axially of said shaft, said first portion beingcylindrical and diametrically enlarged transversely of the axis of saidshaft relative to said second portion, said shaft having a groove in theouter surface thereof extending axially in said diametrically enlargedfirst portion and terminating interiorly of said housing, a plurality ofchange gears freely journaled on said first portion of said shaft withinsaid housing and having key-receiving means, a key within said grooveaxially slidable between successive gear-engaging positions and havingsuccessive interengagements with said key-receiving means of successivegears when axially shifted to successive gear-engaging positions wherebythe selected gear with which said key is interengaged is drivinglycoupled via said key to said shaft, at least one end of said grooveterminating in an axially open end adjacent said second portion topermit said key to be inserted lengthwise into said groove through saidaxially open end thereof, and shift means for axially shifting said keybetween said gear-engaging positions..]. .[.2. The combination of claim1 wherein each gear comprises means forming an arcuate recess in thebore thereof defining said key-receiving means thereof and wherein saidkey comprises a lug normally projecting radially outwardly of saidgroove beyond the surface of said diametrically enlarged portion forsuccessive interengagment with said arcuate recesses of successive gearswhen said key is axially shifted to successive gear-engagingpositions..]. .[.3. The combination of claim 2 wherein said arcuaterecesses of said gears are axially separated to define free spacesbetween adjacent recesses and wherein the axial dimension of said lug isless then the axial dimension of said free spaces to thereby define aneutral position of said key between adjacent gear-engaging positionsthereof whereby when said key is shifted to a neutral position, saidshaft is drivingly disconnected from said gears..]. .[.4. Thecombination of claim 1 wherein said shift means comprises a collarjournaled on said grooved shaft within said housing and axially slidablethereon, said collar embracing a portion of said key, said key and saidcollar having means operatively connecting said collar with said key torender said key axially slidable in unison with said collar, andactuating means operatively connected to said collar for axiallyshifting said collar on said grooved portion..]. .[.5. The combinationof claim 4 wherein said means operatively connecting said key with saidcollar comprises a pair of axially spaced-apart annular surfaces on saidcollar and complementary projection means on said key projectingoutwardly of said groove beyond the outer surface of said grooved shaft,said collar surfaces and said projection means being radially overlappedto restrain relative axial movement between said key and collar..]..[.6. The combination of claim 5 wherein said means operativelyconnecting said actuating means with said collar comprises means forminga central circular groove in the outer surface of said collar and arotary shift arm engaging said groove of said collar such that rotationof said shift arm by said actuating means shifts said collar axially onsaid grooved shaft..]. .[.7. The combination of claim 1 furtherincluding detent means operable with said shift means for correlatingpositions of said shift means to said gear-engaging positions of saidkey..].
 8. .[.The combination of claim 7 wherein said shift meanscomprises a rotary shift shaft journaled in said housing and said.]..Iadd.In a transmission including a housing having opposite end wallsand side walls, a shaft having first and second portions extendingaxially of said shaft, said first portion being intermediate said secondportions and being cylindrical and diametrically enlarged transverselyof the axis of said shaft relative to said second portions, said secondportions of said shaft being respectively journaled in said housing endwalls, said shaft having a groove in the outer surface thereof extendingaxially in said diametrically enlarged first portion and terminatinginteriorly of said housing, a plurality of speed-changing gears freelyjournaled on said first portion of said shaft within said housing andhaving key-receiving means, a key within said groove axially slidablebetween successive gear-engaging positions and having successiveinterengagements with said key-receiving means of successive gears whenaxially shifted to successive gear-engaging positions whereby theselected gear with which said key is interengaged is drivingly coupledvia said key to said shaft, at least one end of said groove terminatingin an axially open end adjacent one said second portion to permit saidkey to be inserted lengthwise into said groove through said axially openend thereof, a rotary shift shaft journaled in said housing side wallsand extending thereacross, means including a shift fork on said shiftshaft and rotatable therewith, and a collar slideably mounted on saidfirst shaft portion operatively connected to said key for axiallyshifting said key between said gear-engaging positions said shift forkengaging said collar for axially shifting the same: .Iaddend.detentmeans .[.comprises.]. .Iadd.in said housing comprising .Iaddend.a rotary.Iadd.plate .Iaddend.member on said shift shaft .Iadd.in said housing.Iaddend.having .[.a.]. .Iadd.an arcuate edge .Iaddend.portion radiallyspaced from said shift shaft for movement opposite a portion of saidhousing, a detent-seat-engaging member .Iadd.in said housing.Iaddend.between said .[.two.]. .Iadd.arcuate edge and housing portions.[.biased.]..Iadd., and spring means in said housing biasing saiddetent-seat-engaging member .Iaddend.radially .[.of.]..Iadd.toward.Iaddend.said shift shaft and a plurality of angularly spaced-apartfirst detent seats in .[.one of said portions.]. .Iadd.said edge portionof said plate member.Iaddend., said detent-seat-engaging member havingselective engagements with said first detent seats in accordance withthe rotary position of said shift shaft to thereby correlate the rotarypositions of said shift shaft with the gear-engaging positions of saidkey. .[.9. The combination of claim 8 wherein said detent means iswithin said housing..].
 10. The combination of claim 8 wherein .[.saidrotary member comprises a plate having a generally arcuate edge portionradially spaced from said shift shaft, said plurality of first seatsbeing formed in said edge of said plate,.]. said detent-seat-engagingmember .[.comprising.]. .Iadd.comprises .Iaddend.a ball biased inwardlytoward said shift shaft for engagement one at a time with said firstseats.
 11. The combination of claim 10 wherein said detent means furthercomprises means forming a plurality of second detent seats in said plateeach having a radial alignment with said shift shaft and those of saidfirst detent seats correlated to neutral positions of said key, saidsecond seats being arcuately arranged at a selected radial distance fromsaid shift shaft, and a switch on said housing having a switch actuatorbiased toward said plate for selective engagement with said second seatsin accordance with the angular position of said shift shaft, said switchbeing operable in response to engagement of said switch actuator withsaid second seats to thereby correlate switch operation to the neutralpositions of said key.
 12. .[.The combination of claim 7 wherein.]..Iadd.In a transmission including a housing having opposite end wallsand side walls, a shaft having first and second portions extendingaxially of said shaft, said first portion being intermediate said secondportions and being cylindrical and diametrically enlarged transverselyof the axis of said shaft relative to said second portions, said secondportions of said shaft being respectively journaled in said housing endwalls, said shaft having a groove in the outer surface thereof extendingaxially in said diametrically enlarged first portion and terminatinginteriorly of said housing, a plurality of speed-changing gears freelyjournaled on said first portion of said shaft within said housing andhaving key-receiving means, a key within said groove axially slidablebetween successive gear-engaging positions and having successiveinterengagements with said key-receiving means of successive gears whenaxially shifted to successive gear-engaging positions whereby theselected gear with which said key is interengaged is drivingly coupledvia said key to said shaft, at least one end of said groove terminatingin an axially open end adjacent one said second portion to permit saidkey to be inserted lengthwise into said groove through said axially openend thereof, a rotary shift shaft journaled in said housing side wallsand extending thereacross, means including a shift fork on said shiftshaft and rotatable therewith, a collar slideably mounted on said firstshaft portion for axially shifting said key between said gear-engagingpositions, said shift fork engaging said collar for axially shifting thesame: detent means in said housing operable with said axially shiftingmeans for correlating positions of said shifting means to saidgear-engaging positions of said key, said detent means .[.comprises.]..Iadd.comprising .Iaddend.a plate .Iadd.on said shift shaft androtatable therewith .Iaddend..[., means for supporting said plate onsaid housing for rotary movement about a fixed axis.]., said platehaving .Iadd.an arcuate edge radially spaced from the axis of said shiftshaft with a plurality of angularly spaced-apart detent seats therein,means including a spring in said housing for providing selectiveengagement with said detent seats in accordance with the rotary positionof said plate, said plate having at least one opening therein spacedradially inwardly from said edge toward said axis .[.switch actuatordisplacement means movable therewith and disposed at a selected radialdistance from said axis.]., and a switch on said housing having a switchactuator biased toward said plate for selective engagement with said.[.displacement means.]. .Iadd.opening .Iaddend.in accordance with theangular position of said plate, said switch being operable in responseto engagement of said switch actuator with said .[.displacement means.]..Iadd.opening .Iaddend.to thereby correlate switch operation to aneutral position of said key. .[.13. The combination of claim 12 whereinsaid detent means is within said housing..]. .[.14. The combination ofclaim 1 wherein said shift means comprises a collar journaled on saiddiametrically enlarged portion of said shaft and axially slidablethereon, means operatively connecting said collar with said key torender said key axially slidable in unison with said collar and meansfor axially shifting said collar on said shaft..]. .[.15. Thecombination of claim 14 wherein said means operatively connecting saidcollar with said key comprises a pair of axially spaced projections onsaid key projecting radially outwardly of said groove and extendingbeyond the outer surface of said diametrically enlarged portion of saidshaft, said collar being axially trapped between said twoprojections..]. .[.16. The combination of claim 15 wherein said meansfor shifting said collar comprises a rotary member journaled in saidhousing, means forming a central circular groove in the outer surface ofsaid collar and means on said member engaging said groove such thatrotary movement of said member shifts said collar axially on saidshaft..]. .[.17. The combination of claim 15 wherein said key furthercomprises a third projection normally projecting radially outwardly ofsaid groove beyond the outer surface of said shaft and axially spacedfrom said pair of projections, said third projection having successiveinterengagements with said key-receiving means of successive gears whensaid key is axially shifted to successive gear-engaging positions byaxially shifting said collar on said shaft..]. .[.18. The combination ofclaim 17 wherein said shift means comprises a collar journaled on saidshaft and axially slidable thereon, said collar encircling said key andbeing spaced axially between said two projections, means operativelyconnecting said collar with said key to render said key axially slidablein unison with said collar and means for axially sliding said collar onsaid shaft..]. .[.19. The combination of claim 18 wherein said meansoperatively connecting said collar with said key comprises a thirdprojection on said key projecting radially outwardly of said groovebeyond the outer surface of said shaft, said collar being axiallytrapped between said third projection and one of saidfirst-two-mentioned projections..]. .[.20. The combination of claim 19wherein said means for axially shifting said collar comprises meansforming a central circular groove in the outer surface of said collarand a rotary member journaled on said housing and engaging said groovesuch that when said member rotates, said collar slides on said shaft..].21. In a transmission, the combination comprising a housing .Iadd.havingopposite end walls and side walls.Iaddend., a shaft journaled in saidhousing .Iadd.end walls .Iaddend.and having a groove in the outersurface thereof extending axially thereof, said groove terminatingwithin said housing, key means within said groove and axially slidabletherein, a plurality of .[.change.]. .Iadd.speed-changing .Iaddend.gears.Iadd.and an additional gear .Iaddend.journaled on said shaft withinsaid housing .[.at least one of which is.]..Iadd.with said additionalgear .Iaddend.adjacent one end of said key means, said change .Iadd.andadditional .Iaddend.gears having key-receiving means therein associatedwith said groove of said shaft, said key means having a pair of axiallyspaced-apart lug means normally projecting outwardly of said groovebeyond an outer surface of said shaft when engaged with key-receivingmeans of said gears, .[.said lug means being spaced axially apart suchthat.]. said lug means .[.are.]. .Iadd.being .Iaddend.disengaged fromall of said key-receiving means of said change gears and said additionalgear when said key means is in a neutral position wherein all of saidgears are drivingly disconnected from said shaft, .Iadd.one of.Iaddend.said lug means .Iadd.being .Iaddend.adjacent said change gears.Iadd.and .Iaddend.having successive interengagements with saidkey-receiving means of successive change gears as said key means isaxially shifted .Iadd.in one direction .Iaddend.from said neutralposition toward said change gears, .Iadd.the other of .Iaddend.said lugmeans .Iadd.being .Iaddend.adjacent said additional gear .Iadd.and.Iaddend.having an interengagement with said key-receiving means of saidadditional gear when said key means is axially shifted .Iadd.in theopposite direction .Iaddend.from said neutral position toward saidadditional gear, and shift means .Iadd.including a rotary shift shaftjournaled in said housing side walls and extending thereacross, a shiftfor on said shift shaft and rotatable therewith, a collar slideablymounted on said first-named shaft connected to said key meansintermediate said lug means .Iaddend.for axially shifting said key meansinto said neutral and gear-engaging positions, whereby the selected gearwith which said key means is interengaged .[.in.]. .Iadd.is.Iaddend.drivingly coupled via said key means to said shaft .Iadd.saidshift fork engaging said collar for axially shifting the same.Iaddend..22. In a transmission, the combination comprising .Iadd.a housingenclosing .Iaddend.a shaft, a plurality of .Iadd.speed-changing.Iaddend.gears, means for driving said gears, shift means including ashift member movable between successive gear-engaging positions foroperatively connecting said gears one at a time to said shaft, saidshift member having neutral positions separating adjacent gear-engagingpositions wherein said gears are drivingly disconnected from saidshaft.Iadd., said shift means further including a rotary shift shaft, acollar slideably mounted on said first-named shaft and connected to saidshift member, a shift fork on said shift shaft and rotatable therewith,said shift fork engaging said collar, .Iaddend.and detent means forcorrelating the neutral positions of said shift member to certainpositions of said shift means comprising a .Iadd.rotary .Iaddend.plate.Iadd.on said shift shaft operatively connected to said shift member andmovable therewith.Iaddend., means forming a plurality of seats in saidplate, a switch having a switch actuator biased twoard said plate andmovable between an actuated position and a nonactuated position .[.andmeans movable with said shift member for moving said switch actuatorrelative to said plate such that.]. .Iadd.in response to movement ofsaid plate whereby .Iaddend.said actuator successively engages saidseats, said actuator being operated to one of its positions when engagedwith said seats and operated to its other position when disengaged fromsaid seats, the arrangement of said seats of said plate being such thatsaid actuator is operated to one of its positions by said plate whensaid shift member is in said neutral positions whereby switch operationis correlated to said neutral positions. .[.23. The combination of claim22 wherein said plate is movable with said shift member..]. .[.24. Thecombination of claim 23 wherein said shift member is journaled forrotation about a fixed axis and wherein the plane of said plate isperpendicular to said shift member, said seats being angularly spacedapart in said plate at a selected radial distance from said axis..]. 25.The combination of claim .[.24 further including additional detentmeans.]. .Iadd.22 wherein said plate has means forming an additionalplurality of seats therein .Iaddend.for correlating additional positionsof said shift means to the gear-engaging positions of said shift member..[.26. The combination of claim 1 wherein the material of said gearscomprises a sintered powdered metal consisting of iron pre alloy havingsubstantially the following percentage composition by weight: Nickel(0.45 percent); Molybdenum (0.60 percent); Manganese (0.35 percent);Sulfur (0.010 percent); Phosphorus (0.010 percent); Iron (Balance);Carbon (0.5/0.6 percent) and having a minimum density of 6.7grams/c.c..]. .[.27. The combination of claim 1 wherein said gearscomprise a sintered ferrous powdered metal material..]. .[.28. In atransmission, the combination comprising a shift, journal means forsupporting said shaft for rotation about its axis, a collar slidablyreceived on a first portion of said shaft, said shaft having a groove inthe outer surface thereof extending axially of said shaft, a pluralityof change gears journaled on said shaft and having key-receiving means,a key within said groove axially slidable between successivegear-engaging positions and having means thereon operable tosuccessively interengage said key-receiving means of said gears whensaid key is axially shifted to successive gear-engaging positionswhereby the selected gear with which said key is interengaged isdrivingly coupled via said key to said shaft, a pair of axiallyspaced-apart retainer lugs on said key projecting outwardly of saidgroove beyond an outer surface of said shaft, said collar encirclingsaid key and being axially trapped between said pair of retainer lugs torender said key axially slidable in unison with said collar, said shafthaving a circumferentially extending face extending inwardly radially ofsaid shaft from said outer surface thereof and terminating in an axiallyopen end at said face to thereby permit slip-on assembly of said key andsaid collar to said shaft by endwise insertion of the subassembly ofsaid key in said collar with said collar trapped between said pair ofretainer lugs when said collar is concentrically aligned with said shaftand said key is angularly aligned with said open end of said groove topermit said subassembly to be moved generally axially onto said shaftsuch that said collar in assembly is received on said first portion ofsaid shaft, and shift means for axially shifting said collar on saidshaft to thereby shift said key to said gear-engaging positions..]..[.29. The combination of claim 28 wherein said shaft has second andthird portions having uninterrupted cylindrical surfaces, and saidjournal means likewise has uninterrupted first and second cylindricalbores respectively receiving said second and third portions with a closerunning fit, said transmission being enclosed in a closed housing withsaid journal means being mounted with a seal fit in outer walls of saidhousing and said shaft protruding from said housing via at least one ofsaid journal means..]. .[.30. The combination of claim 29 wherein saidmeans on said key operable to successively engage said key-receivingmeans of said gears comprises a third lug having successiveinterengagements with said key-receiving means of said gears when saidkey is axially shifted to successive gear-engaging positions..]. .[.31.The combination of claim 30 wherein said third lug comprises axiallyspaced-apart end surfaces and side surfaces extending axially betweensaid end surfaces, said side surfaces being connected in part to saidend surfaces by outwardly-extending beveled edges..]. .[.32. Thecombination of claim 29 wherein said face is defined by a shoulder at ajunction of said first portion with one of said second and thirdportions, said cylindrical surface of said one portion having a radiusequal to or less than the radial distance between the axis of said shaftand a bottom surface of said groove..]. .[.33. In a transmission, thecombination comprising a housing defining a completely enclosed gearchamber within said housing and having first and second spaced wallsdefining opposite sides of said housing, a shaft having axially spacedjournal portions having uninterrupted cylindrical surfaces, first andsecond sealing means in said first and second side walls respectivelyhaving uninterrupted cylindrical bores respectively receiving said firstand second journal portions with a close running fit for journaling saidshaft in said housing side walls, said shaft having a groove in theouter surface thereof extending axially thereof and terminatinginteriorly of said housing between said journal portions, a plurality ofchange gears journaled on said shaft within said housing chamber andhaving key-receiving means, a key within said groove axially slidablebetween successive gear-engaging positions and having successiveinterengagements with said key-receiving means of successive gears whenaxially shifted to successive gear-engaging positions whereby theselected gear with which said key is interengaged is drivingly coupledvia said key to said shaft, and shift means within said chamber foraxially shifting said key between said gear-engaging positions..]..[.34. The combination of claim 33 wherein said shaft has akey-receiving portion within said housing having a diameter larger thanat least one of said journal portions, said groove extending axially insaid key-receiving portion and said shaft having a root surface definingthe base of said groove spaced radially outwardly from the axis of saidshaft at least flush with the cylindrical surface of at least one ofsaid journal portions..]. .[.35. The combination of claim 34 whereinsaid housing comprises a case and a cover separable from one another andhaving mutually mating surfaces defining edges of said side wallsabutted in the closed condition of said housing, said sealing meansbeing disposed in said edges such that the axis of said shaft issubstantially coincident with said surfaces..].
 36. .[.The combinationof claim 1 wherein.]. .Iadd.In a transmission including a housing, ashaft journaled in said housing, said shaft having first and secondportions extending axially of said shaft, said first portion beingcylindrical and diametrically enlarged transversely of the axis of saidshaft relative to said second portion, said shaft having a groove in theouter surface thereof extending axially in said diametrically enlargedfirst portion and terminating interiorly of said housing, a plurality ofspeed-changing gears freely journaled on said first portion of saidshaft within said housing and having key-receiving means, a key withinsaid groove axially slidable between successive gear-engaging positionsand having successive interengagements with said key-receiving means ofsuccessive gears when axially shifted to successive gear-engagingpositions whereby the selected gear with which said key is interengagedis drivingly coupled via said key to said shaft, at least one end ofsaid groove terminating in an axially open end adjacent said secondportion to permit said key to be inserted lengthwise into said groovethrough said axially open end thereof, and shift means for axiallyshifting said key between said gear-engaging positions, each of.Iaddend.of said change gears .[.has.]. .Iadd.having .Iaddend.an axialbore therethrough by which it is journaled on said shaft.[.,.]..Iadd.:.Iaddend.said key-receiving means of at least one of said change gears.[.comprises.]. .Iadd.comprising .Iaddend.at least one recess thereinextending radially outward of said bore and opening into said bore, saidrecess having a pair of generally axially extending abutments therein ingenerally opposed arcuately spaced relation to each other with one ofsaid abutments terminating in said recess radially outward of said bore.Iadd.and the other of said abutments forming one end wall of saidrecess, said abutments defining a key-receiving slottherebetween.Iaddend., said key comprises a lug movable both axially ofsaid shaft to successive gear-engaging positions to underlie each ofsaid gears having said recess therein and generally radially outward ofthe portion of said shaft on which said change gears are journaled into.[.recess.]. .Iadd. slot .Iaddend.between the abutments of an associatedchange gear overlying said lug to drivingly couple via said key saidchange gears one at a time with said shaft for rotation therewith thetransverse width of the portion of said lug receivable .Iadd.in saidslot .Iaddend.between said abutments being dimensioned in relation tothe generally arcuate spacing between said abutments such that when saidlug is received .[.between the abutments of a recess.]. .Iadd.in saidslot .Iaddend.of an associated change gear there can be substantially norelative rotation between an associated change gear and said shaft,.[.and .]. .Iadd.said .Iaddend.at least one .[.of said recesses.]..Iadd.recess .Iaddend.at its associated bore having a generally arcuatelength encompassing said abutments and extending beyond said oneabutment .Iadd.to the other end wall of said recess .Iaddend.by adistance at least substantially one quarter of the transverse width ofthe portion of said lug .Iadd.thereby defining a step extending axiallybetween said one abutment and said other end wall, said step having asurface disposed radially outwardly of said bore.Iaddend., whereby bothbacklash between the change gear coupled with said shaft for rotationtherewith and said shaft is eliminated and said lug can be readily fullyreceived between the abutments of a change gear when coupling a rotatingchange gear with said shaft for rotation therewith. .[.37. Thecombination of claim 1 wherein said key comprises a lug which whenreceived in said groove continuously projects radially outwardly of saidgroove beyond the outer surface of the portion of the shaft on whichsaid change gears are journaled, said key-receiving means of said gearscomprising passages extending axially through said change gears open atthe axially opposite ends thereof to receive said lug so that said lugis shiftable axially in said passages when said key is axially shiftedto successive gear-engaging positions..]. .[.38. The combination ofclaim 1 wherein said key comprises a resilient metallic arm with a lugadjacent one end thereof, said key being slidably received in saidgroove for generally axial movement therein with said arm yieldablyurging said lug radially outwardly of the portion of said shaft on whichsaid change gears are journaled..].
 39. The combination of claim 21wherein said key means also comprises a resilient metallic arm integralwith and interposed between said axially spaced apart lug means withsaid lug means adjacent said change gears being carried by saidinherently resilient arm adjacent the free end thereof and beingyieldably urged by said arm radially outwardly of the portion of saidshaft on which said change gears are journaled.
 40. .[.The combinationof claim 28 wherein.]. .Iadd.In a transmission including a housinghaving opposite end and side walls, a shaft, journal means in saidhousing and walls for supporting said shaft for rotation about its axis,a collar slidably received on a first portion of said shaft in saidhousing, said shaft having a groove in the outer surface thereofextending axially of said shaft, a plurality of speed-changing gearsjournaled on said shaft in said housing and having key-receiving means,a key within said groove axially slidable between successivegear-engaging positions and having means thereon operable tosuccessively interengage said key-receiving means of said gears whensaid key is axially shifted to successive gear-engaging positionswhereby the selected gear with which said key is interengaged isdrivingly coupled via said key to said shaft, a pair of axiallyspaced-apart retainer lugs on said key projecting outwardly of saidgroove beyond an outer surface of said shaft, said collar encirclingsaid key and being axially trapped between said pair of retainer lugs torender said key axially slidable in unison with said collar, said shafthaving a circumferentially extending face extending inwardly radially ofsaid shaft from said outer surface thereof and terminating in an axiallyopen end at said face to thereby permit slip-on assembly of said key andsaid collar to said shaft by endwise insertion of the subassembly ofsaid key in said collar with said collar trapped between said pair ofretainer lugs when said collar is concentrically aligned with said shaftand said key is angularly aligned with said open end of said groove topermit said subassembly to be moved generally axially onto said shaftthat said collar in assembly is received on said first portion of saidshaft, and shift means including a rotary shift shaft journaled in saidhousing side walls and extending thereacross and a shift fork on saidshift shaft rotatable therewith and engaging said collar .Iaddend.foraxially shifting said collar on said shaft to thereby shift said key tosaid gear-engaging positions: said key also .[.comprises.]..Iadd.comprising .Iaddend.a resilient metallic arm integrally connectedwith said pair of axially spaced apart lugs adjacent one end of saidarm.Iadd., .Iaddend.and said means operable to successively interengagesaid key-receiving means .[.comprises.]. .Iadd.comprising .Iaddend.athird lug carried by said arm adjacent the other end thereof andintegral therewith, said arm yieldably urging said third lug radiallyoutwardly of the portion of said shaft on which said change gears arejournaled.Iadd., the resilience of said arm being the sole force urgingsaid third lug outwardly.Iaddend..
 41. The combination of claim 36wherein said key also comprises a resilient metallic arm, said lug beingintegral with said arm and adjacent one end thereof, said key beingslidably received in said .[.grooves.]. .Iadd.groove .Iaddend.forgenerally axial movement therein with said arm yieldably urging said lugradially outwardly of the portion of said shaft on which said changegears are journaled. .[.42. The combination of claim 36 wherein each ofsaid change gears comprises sintered powdered iron having a minimumdensity of 6.7 grams per cubic centimeter..].
 43. The combination ofclaim 36 wherein each said recess in each of said gears extendsgenerally axially throughout each of said gears and which also comprisesa washer carried by each of said change gears adjacent one face thereofand having an inner peripheral portion forming an end wall in each ofsaid recesses to thereby close each said recess at the end thereofadjacent said one face. .[.44. The combination of claim 43 wherein eachof said change gears comprises sintered powdered iron having a minimumdensity of 6.7 grams per cubic centimeter and has a counterbore thereinopening into one face thereof with said counterbore therein opening intoone face thereof with said counterbore being formed therein prior tosintering of the powdered iron thereof, and said washer of each of saidchange gears is fixedly received in said counterbore thereof..].
 45. Ina transmission, the combination comprising a housing, a shaft journaledin said housing, a plurality of separate .[.change.]..Iadd.speed-changing .Iaddend.gears each having an axial boretherethrough journaled on a portion of said shaft for free rotationrelative thereto, at least one of said gears having a recess thereinextending radially outward of said bore.Iadd., said recess havingopposite end walls .Iaddend.and opening into said bore and a pair ofgenerally axially extending .[.in at least one of said recesses ingenerally opposed arcuately spaced relation to each other with one ofsaid abutments terminating in said recess radially outward of said bore.Iadd.and the other abutment being at one of said end walls, saidabutments defining a key-receiving slot therebetween.Iaddend., and keymeans having a lug carried by said shaft for rotation therewith, saidlug being movable both generally axially of said shaft to selectivelyunderlie each of the gears having an associated pair of abutments andgenerally radially outwardly of said shaft portion into a registered.[.recess.]. .Iadd.slot .Iaddend.between abutments thereof to couplesaid change gears having an associated pair of abutments one at a timewith said shaft for rotation therewith, said lug having a transversewidth slightly less than the spacing between said abutments of each.[.recess.]. .Iadd.slot .Iaddend.to thereby minimize relative rotationbetween said shaft and the selected change gear when said lug isreceived .Iadd.in said slot .Iaddend.between said abutments thereof, andeach of said recesses with an associated pair of abutments having at itsassociated bore a generally arcuate length .Iadd.between opposite endwalls .Iaddend.encompassing said abutments and extending beyond said oneabutment .Iadd.to the other end wall of said recess .Iaddend.by adistance at least substantially one quarter of the transverse width ofsaid lug .Iadd.thereby defining a step extending arcuately between saidone abutment and said other end wall, said step having a surfacedisposed radially outwardly of said bore .Iaddend.whereby both back-lashbetween said shaft and the change gear coupled with said shaft forrotation therewith is eliminated and said lug can be readily fullyreceived between the abutments of a change gear when coupling a rotatingchange gear with the shaft for rotation therewith. .[.
 6. Thecombination of claim 45 wherein each of said recesses has a step thereinadjacent said one abutment, said step having a surface disposed radiallyoutwardly of said bore extending generally arcuately from said oneabutment to the circumferential end of said recess remote from the otherof said abutments..].
 47. The combinatioon of claim 45 whereincircumferential length of each recess at its associated bore is at leastand one half times the circumferential spacing between said abutments.48. The combination of claim 45 wherein the circumferential length ofsaid recess at its associated bore is in the range of one and onequarter to twice the circumferential spacing beteeen said abutments. .The combination of claim 45 including means forming a groove in theouter surface of said shaft extending axially thereof and wherein saidkey means comprises a key having a resilient arm with said lug beingintegral with said arm adjacent a free end thereof, said key beingslidably received in said groove for generally axial movement thereinwith said arm yieldably urging said lug to a position wherein said lugprotrudes radially outwardly of said shaft portion and said lug isspaced from the bottom of said groove.
 50. The combination of claim 49wherein each of said recesses extends generally axially throughout itsassociated change gear and which also comprises a washer carried by eachof said change gears adjacent one face thereof and having an innerperipheral portion closing the end of said recess adjacent said oneface, whereby said washers cooperate with said lug to shift said luggenerally radially inwardly against the bias of said resilient arm todisengage said lug from a recess of a change gear when said lug is movedaxially past said washer whereby the change gear is decoupled from saidshaft.
 51. The combination of claim 50 wherein .[.each of.]. said lughas two generally opposed ramps on edge faces of said lug with saidramps being inclined with respect to each other and converging radiallyoutwardly of said lug, said ramps being adapted to bear on said washersto disengage said lug from said recess in said change gears when saidlug is moved axially past said washers.
 52. The combination of claim 51wherein said key comprises a shank connected to the end of said armremote from its free end, said shank having a flat bottom surface layingflat on the bottom surface of said groove, said arm extending at agradual angle from shank away from the bottom surface of said groove soas to function as a cantilever spring arm. .[.53. The combination ofclaim 52 wherein said change gears comprise sintered powdered iron andsaid washers comprise sheet metal stampings..].
 4. The combination ofclaim .[.53.]. .Iadd.52 .Iaddend.wherein each of said change gears has acounterbore therein opening into one face thereof .[.with saidcounterbore being formed therein when compacting the powdered ironthereof.]., and the associated washer is located in said counterbore..[.55. The combination of claim 54 wherein each of said washers is madeof case hardened high carbon steel..]. .[.56. The combination of claim55 wherein said washers are fixed to said change gears by the sinteringof the powdered iron thereof..].
 57. The combination of claim .[.51.]..Iadd.52 .Iaddend.wherein said key comprises a one-piece member withsaid lug and said arm being homogeneously integral, said arm being acontinuatioon of said shank and being bent with permanent deformation toincline said arm to slope generally radially outwardly as it extendsfrom said shank to said free end of said arm.
 58. The combination ofclaim 57 wherein the bend in said arm is axially spaced from said shankto thereby increase the fatigue resistance of said one-piece key. 59.The combination of claim 58 wherein said bend is spaced from said shankat least substantially one-fourth of an inch.
 60. The combination ofclaim 58 wherein said shank has second and third spaced lugs protrudingtherefrom beyond the outer surface of said shaft, and wherein a collarencircles said shaft and is trapped between said second and third lugsto provide means for shifting said key axially of said shaft.
 61. Thecombination of claim 21 wherein said shaft has first and second portionsextending axially of said shaft, said first portion being cylindricaland diametrically enlarged transversely of the axis of said shaftrelative to said second portion, and said groove extends axially in aiddiametrically enlarged first portion with at least one end of saidgroove terminating in an axially open end adjacent said second portionto permit said key means to be inserted lengthwise into said groovethrough said axially open end thereof. .[.62. The combination of claim33 wherein said shaft has first and second portions extending axially ofsaid shaft, said first portion being cylindrical and diametricallyenlarged transversely of the axis of said shaft relative to said secondportion, and said groove extends axially in said diametrically enlargedfirst portion with at least one end of said groove terminating in anaxially open end adjacent said second portion to permit said key to beinserted lengthwise into said groove through said axially open endthereof..]. .[.63. The combination of claim 1 wherein said housingdefines a completely enclosed gear chamber within said housing and hasfirst and second spaced walls defining opposite sides of said housingand said shaft has axially spaced journal portions having uninterruptedcylindrical surfaces, and the combination further comprises first andsecond sealing means in said first and second side walls respectivelyhaving uninterrupted cylindrical bores respectively receiving said firstand second journal portions with a close running fit for journaling saidshaft in said housing side walls, said groove extending axially of saidshaft terminates interiorly of said housing between said journalportions..]. .[.64. The combination of claim 21 wherein said housingdefines a completely enclosed gear chamber within said housing and hasfirst and second spaced walls defining opposite sides of said housing,and said shaft has axially spaced journal portions having uninterruptedcylindrical surfaces, and the combination further comprises first andsecond sealing means in said first and second side walls respectivelyhaving uninterrupted cylindrical bores respectively receiving said firstand second journal portions with a close running fit for journaling saidshaft in said housing side walls, said groove extending axially of saidshaft terminates interiorly of said housing between said journalportions..]. .[.65. The combination of claim 61 wherein said housingdefines a completely enclosed gear chamber within said housing and hasfirst and second spaced walls defining opposite sides of said housingand said shaft has axially spaced journal portions having uninterruptedcylindrical surfaces, and the combination further comprises first andsecond sealing means in said first and second side walls respectivelyhaving uninterrupted cylindrical bores respectively receiving said firstand second journal portions with a close running fit for journaling saidshaft in said housing side walls, said groove extending axially of saidshaft terminates interiorly of said housing between said journalportions..]. .Iadd.66. In a transmission including a housing havingopposite end walls and side walls, a shaft having first and secondportions extending axially of said shaft, said first portion beingintermediate said second portions and being cylindrical anddiametrically enlarged transversely of the axis of said shaft relativeto said second portions, said second portions of said shaft beingrespectively journaled in said housing end walls, said shaft having agroove in the outer surfaces thereof extending axially in saiddiametrically enlarged first portion and terminating interiorly of saidhousing, a plurality of speed-changing gears freely journaled on saidfirst portion of said shaft within said housing and having key-receivingmeans, a key within said groove axially slidable between successivegear-engaging positions and having successive interengagements with saidkey-receiving means of successive gears when axially shifted tosuccessive gear-engaging positions whereby the selected gear with whichsaid key is interengaged is drivingly coupled via said key to saidshaft, at least one end of said groove terminating in an axially openend adjacent said second portion to permit said key to be insertedlengthwise into said groove through said axially open end thereof, andshift means a shift fork on said shift shaft and rotatable therewith, acollar slideably mounted on said shaft portion and connected to said keyfor axially shifting said key between said gear-engaging positions, saidshift fork engaging said collar for axially shifting the same; said keycomprising a resilient metallic arm with a lug adjacent one end thereof,said lug having two generally opposed ramps on edge faces thereof withsaid ramps being inclined with respect to each other and convergingradially outwardly of said lug, said key comprising a shank connected tothe end of said arm remote from the lug end, said shank having a bottomsurface lying flat on the surface of said groove, said arm extending ata gradual angle from the shank away from the bottom surface of saidgroove so as to function as a cantilever spring arm with the lug near afree end thereof, said key being slidably received in said groove forgenerally axial movement therein with said arm yieldably urging said lugradially outwardly of the portion of said shaft on which said changegears are journaled, the resilience of said arm being the sole forceurging said lug outwardly each of said key-receiving means comprises arecess extending generally axially throughout its associated changegear, a washer associated with each of said change gears adjacent oneface thereof and having an inner peripheral portion closing the end ofsaid recess adjacent said one face, whereby said washers cooperate withsaid lug to shift said lug generally radially inwardly against the biasof said resilient arm to disengage said lug from a recess of a changegear when said lug is moved axially past said washer whereby the changegear is decoupled from said shaft, said lug ramps being adapted to bearon waid washers to disengage said lug from said recess in said changegears when said lug is moved axially past said washers. .Iaddend..Iadd.67. The combination of claim 66 wherein said key comprises aone-piece member with said lug and said arm being homogeneouslyintegral, said arm being a continuation of said shank and being bentwith permanent deformation to incline said arm to slope generallyradially outwardly as it extends from said shank to said free end ofsaid arm. .Iaddend. .Iadd.68. The combination of claim 67 wherein thebend in said arm is axially spaced from said shank to thereby increasethe fatigue resistance of said one-piece key. .Iaddend. .Iadd.69. Thecombination of claim 66 wherein each of said change gears has acounterbore therein opening into one face thereof, and the associatedwasher is located in said counterbore. .Iaddend.